The present invention relates to an automobile mirror system in which the automobile interior and exterior rearview mirrors differ in reflectivity, particularly to an anti-glare mirror system in which the interior rearview mirror has a lower reflectivity than the exterior rearview mirror.
During night driving, drivers sometimes experience glare from the interior rearview mirror (hereinafter referred to as "IM") and the exterior or outside rearview mirror ("OM") of their cars due to reflected light from the following cars. To prevent this, anti-glare mirror systems have been invented.
These anti-glare mirror systems use an electrochromic device (hereinafter referred to as "ECD"), a liquid crystal device ("LCD"), or other means.
The ECD has the property of changing between a colored and a bleached state by reversible reaction in response to a change in the polarity of the current applied to it. Utilizing this property, the ECD is put in the colored state when it is desired to reduce the mirror reflectivity and in the bleached state when it is desired to increase the reflectivity.
The LCD has the property of changing the orientation of its liquid crystal molecules according to the electric field applied to it. When light enters a liquid crystal with this sort of molecular orientation, the light is polarized and makes complex refraction. Accordingly, the reflectivity can be controlled by controlling the orientation of the liquid crystal.
But the LCD is more difficult to handle and more expensive than the ECD, so that the ECD is more frequently used for the anti-glare mirror systems.
Both liquid-phase ECD and solid-state ECD made from different materials exist. While it is easier to achieve a low reflectivity and economical anti-glare mirror system with a liquid-phase ECD, it has the disadvantages that it has a slower color change reaction than a solid-state ECD, it is chemically unsuitable, it is hard to be apply to curved mirrors.
The basic structure of the liquid-phase ECD consists of a liquid-phase EC layer sandwiched between two sheets of transparent substrates. The opposite side surface of one of the substrates contacting the liquid-phase EC layer is provided with an anti-reflectance coating. The reason that the anti-reflectance coating and the liquid-phase EC layer are installed via the transparent substrate is that the anti-reflectance coating, if it comes into contact with the liquid-phase EC layer, reacts with the acid contained in the layer.
The problem is that the reflection of light in the rearview mirror field can therefore occur by the anti-reflectance coating and the transparent substrate provided with this coating, producing multiple images in the rearview mirror field which can impair the driver's visibility. This impairment of visibility by the occurrence of multiple images becomes remarkable if the light incidence angle in the rearview mirror field differs significantly from its reflection angle, so it is difficult to apply the liquid-phase ECD to the OM.
Meanwhile, if the IM is installed at a location closer to the driver's seat, the IM produces more glare than the OM, so that if both the IM and OM have the same reflectivity, the visibility in the rearview mirror field becomes unbalanced.
In the OM and IM having an ECD with the same members and used under the same operation conditions, the attempt to prevent the IM from producing glare could reduce the reflectivity of the OM, impairing the visibility in the rearview mirror field, while prevention of glare from the OM makes prevention of glare from the IM insufficient. Thus the ECD has conventionally been only used for the IM which has a greater glare than the OM to obtain better visibility in the rearview mirror field.
However the problem with this latter method is that, even if the IM glare can be prevented, the OM glare cannot be eliminated. To solve this problem, the U.M. Journal No. 123836/1989 discloses a method which varies the operating conditions between the IM and OM having the ECD with the same members.
More concretely, the apparatus is structured so that the IM ECD can be colored prior to the OM ECD to activate the anti-glare feature of the mirror system, and the IM ECD can be bleached prior to the OM ECD to make the mirror system turn off the anti-glare feature.
However in this case, though the timing of the coloring differs from that of the bleaching, the IM and OM show the same reflectivity when the ECD has reached saturation conditions after a predetermined time after the start of the coloring or the bleaching, making the driver's visibility unbalanced between the IM and OM.